The present invention relates to probes, and more particularly to optical probes for measuring the intensity and/or intensity distribution of an incident light beam.
Various optical probes have been proposed in the past to measure the intensity of a light beam. Such probes include charged-coupled device (CCD) camera probes, silicon detector probes, photodetector probes, pinhole probes, and knife-edge probes. CCD camera, silicon detector, and photodetector probes have the disadvantage of being relatively large. Their large size limits their application to situations where there is ample space for placing or installing probe instrumentation. Another disadvantage of CCD camera, silicon detector, and photodetector probes is that they all absorb radiation over a small sensitive area, which renders them susceptible to damage when placed in intense or strong optical fields. While pinhole probes and knife-edge probes do not require as large a space for measuring light intensity, they have the disadvantage of blocking and scattering a large portion of an incident light beam to distort the measurement of the intensity of the incident light. Thus, these probes are often not as accurate as desired.
Thus, a need exists for an optical probe whose size can be freely adjusted to be placed in a relatively small space as well as a relatively large space. Such an optical probe, preferably, should not be susceptible to damage when exposed to strong optical fields. Further, such an optical probe should provide an accurate measurement of the intensity and/or intensity distribution of the light beam. The present invention is directed to providing such a probe.
In accordance with the present invention, an optical probe for measuring the intensity and/or intensity distribution of a light beam is provided. An optical probe formed in accordance with one embodiment of the invention includes a substrate formed of nonlight-absorbing material. A light-scattering element is included in the substrate. The light-scattering element has an index of refraction different from that of the substrate. For example, the substrate may be formed of a transparent plastic or glass block and the light-scattering element may be formed of an air bubble trapped within the block. The optical probe further includes an aperture stop for receiving the light scattered by, refracted by, and/or reflected from the light-scattering element. The light-scattering element and the aperture stop are arranged in fixed relationship with respect to each other. The optical probe still further includes a light-measuring device for measuring the intensity of the light received by the aperture stop.
In operation, as an incident light beam enters the substrate, some of the light strikes and is scattered by, refracted by, and/or reflected from the light-scattering element. Some of such light is then received by the aperture stop and then by the light-measuring device. Because the intensity of the incident light beam is proportional to the power of the light received by the aperture stop and transmitted to the light-measuring device, measuring the light collected by the light-measuring device allows the probe to determine the intensity of the incident light. Further, moving the probe with respect to the incident light and measuring the intensity of the light at various locations allows the probe to measure the intensity distribution within the incident light.
Optionally, the optical probe may further include a lens positioned between the light-scattering element and the aperture stop to receive the light scattered by, refracted by, and/or reflected from the light-scattering element. The combination of the lens and the aperture stop isolates the light scattered by, refracted by, and/or reflected from the light-scattering element from the light scattered by, refracted by, and/or reflected from other portions of the optical probe. As a result, only the light from the light-scattering element is received by the light-measuring device, improving the accuracy of the measured incident light.
An optical probe formed in accordance with the present invention may be fabricated in micron scale using various micromachining techniques.
An optical probe formed in accordance with another embodiment of the present invention includes an elongated support having a tip. A light-scattering element is associated with the tip of the elongated support. For example, the elongated support may be formed of a wire and the light-scattering element may be formed of glass attached to the tip of the wire. The optical probe further includes an aperture stop for receiving the light scattered by, refracted by, and/or reflected from the light-scattering element. The light-scattering element and the aperture stop are arranged in fixed relationship with respect to each other. The optical probe still further includes a light-measuring device for measuring the intensity of the light received by the aperture stop.
In operation, the light-scattering element of the optical probe is placed in the propagation path of an incident light beam. As before, some of the incident light beam strikes and is scattered by, refracted by, and/or reflected from the light-scattering element. Some of the light from the light-scattering element is received by the aperture stop and the light-measuring device, allowing the probe to measure the intensity and/or intensity distribution of the incident light.
As with the previous embodiment, optionally, the optical probe may further include a lens so as to isolate the light scattered by, refracted by, and/or reflected from the light-scattering element from the light scattered by, refracted by, and/or reflected from the elongated support, so that only the light from the light-scattering element is received by the light-measuring device.
Also as before, the optical probe of this embodiment may be fabricated in micron scale using various micromachining techniques. A microversion of the optical probe may further include a one-, two-, or three-dimensional microactuator adapted to move the light-scattering element of the optical probe with respect to an incident light beam. This feature allows the intensity distribution within the incident light beam to be measured.
An optical probe formed in accordance with yet another embodiment of the present invention includes a substrate in the form of a sheet (substrate sheet). The optical probe further includes a light-scattering element associated with the substrate sheet, and a light-measuring device for receiving and measuring the light scattered by, refracted by, and/or reflected from the light-scattering element and directed through the substrate sheet. For example, the substrate sheet may be formed of glass, and the light-scattering element may be formed of a void defined on or in the substrate sheet or material having light-scattering property deposited on or in the substrate sheet. This embodiment is suited for measuring the intensity of light propagating between closely spaced optical elements.
In operation, as incident light strikes the surface of the substrate sheet and propagates therethrough, some of the light strikes and is scattered by, refracted by, and/or reflected from the light-scattering element. Some of such light is directed through the substrate sheet and is gathered by the light-measuring device, allowing the probe to measure the intensity of the incident light.
Optionally, the substrate sheet may include polymer dispersed liquid crystal (PDLC) including orthogonally arranged sets of horizontal transparent conductive strips and vertical transparent conductive strips. In this case, the light-scattering element comprises a volume sandwiched between a pair of selected horizontal and vertical transparent conductive strips, between which an electric field is created. Use of PDLC allows the optical probe to selectively position the light-scattering element over the surface area of the substrate sheet.
As before, this embodiment of the optical probe may be fabricated in micron scale using micromachining techniques.
An optical probe formed in accordance with a further alternative embodiment of the present invention includes a substrate sheet that defines a sloped surface, to which an incident light beam is to be directed at an angle. The optical probe further includes a light-measuring device coupled to the substrate sheet for receiving the light scattered by, refracted by, and/or reflected from the sloped surface and directed through the substrate sheet.
In operation, as incident light strikes the substrate sheet and propagates therethrough, some of the light strikes and is scattered by, refracted by, and/or reflected from the sloped surface. This light is directed through the substrate sheet and received by the light-measuring device, allowing the probe to measure the intensity of the incident light.
The space required for an optical probe constructed in accordance with the present invention is on the order of the size of the light-scattering element used. Varying the size of the light-scattering element using various fabrication methods allows optical probes of various sizes to be constructed. For example, using micromachining techniques, an optical probe of a size on the order of microns can be designed. Also, the spatial resolution of the measured intensity distribution map can be freely adjusted by varying the light-scattering element""s size. Because the incident light is scattered by, refracted by, and/or reflected from the light-scattering element, as opposed to necessarily being absorbed by it, and because only the light thus scattered by, refracted by, and/or reflected from the light-scattering element is received by a light-measuring device, a probe formed in accordance with the present invention is not susceptible to damage even when used in relatively strong optical fields. Further, an optical probe of the present invention allows the intensity and/or intensity distribution of an incident light beam to be accurately measured. The invention accomplishes this by isolating the light from a light-scattering element from the stray light from objects other than the light-scattering element. As a result, only the light from the light-scattering element is received by the light-measuring device and intensity measured.